Hundreds of women have taken to the streets of Kenya's capital Nairobi to protest after authorities freed six men suspected of gang-raping a teenager without jailing them.

About 300 women marched through the city on Thursday calling for "justice" and demonstrating against an allegedly unfair ruling in the rape case of the 16-year-old girl known by the psuedonym Liz.

Police arrested the alleged perpetrators but only made them cut grass at the police station as punishment.

Liz was gang-raped and beaten by six men as she returned from her grandfather's funeral in western Kenya in June, before the assailants dumped her, while she was bleeding and unconscious, in a deep sewage ditch.

She is now wheelchair-bound due to spinal problems caused by the sexual assault.

More than 1.3 million people have signed a petition calling for the prosecution of the alleged rapists and an investigation of the police who released the suspects.

Nebila Abdulmelik, of the women's rights campaign group Femnet, launched the petition on Monday.

"Our immediate task is for the arrest and prosecution of the perpetrators, and then disciplinary action at the police who failed to take action, because we feel that they embolden others to rape," Abdulmelik said.

"We are using Liz's story to bring to light all the other cases of violence that are not necessarily reported to the media, to the police."

Source: Agencies